We can deal with Asian rust and stay in soybean production

With the fervor of an old-time tent revivalist exhorting his audience to resist Satan's wiles, Billy Moore tells farmers they can be triumphant in the battle against Asian soybean rust.

What it takes, says the Mississippi Extension professor/plant pathologist emeritus, is knowing your enemy, being alert to what's going on in your soybean fields, and making use of the effective weapons — fungicides — available to fight the disease.

“Rust is nothing to be scared of,” Moore says. “It can be managed with the right tools. We can deal with this disease and still stay in the soybean business,” he told northwest Mississippi growers at recent meetings. “When we were first told we were faced with the threat of soybean rust in the U.S., there were a lot of scary predictions that it could slash yields 40 percent or more, but that's just not going to happen.

“When those predictions were made, there were no fungicides that could do a good job of rust prevention. But the EPA has cleared several and we could possibly have three to four new fungicides available before the 2006 season gets under way. In my 40 years, I have not seen the EPA act so expeditiously in approving products, or so much cooperation between state and federal agencies.”

Further, he said, “There have been no turf battles since this problem has arisen; northern and southern producers have cooperated in detection and management programs, and extensive publicity efforts have kept growers well-informed about the disease.”

One good thing to come out of the soybean rust scare, Moore said, is that “for the first time for a lot of soybean producers, we've seen them climb down out of their pickup trucks and actually look at their soybean fields to see what's going on.

“Some of them have had other diseases present for years and have been seeing them for the first time because they were looking for soybean rust. And that's a positive development.”

Although soybean rust was first identified in Japan in 1902, and had traveled across the ocean to South America by 2000-01, it was not until September 2004 that Hurricane Ivan picked up spores and deposited them in a nine-state area in the southern United States — significantly advancing the timetable that had been predicted for the disease to reach this country.

While that was a wakeup call for the U.S. soybean industry, Moore said, the threat posed by the disease was sometimes overblown.

“Soybean rust is all over South America, but producers there have learned to live with it because they have effective control measures. If they can live with it, we can too, because we have better circumstances for dealing with it. They have year-round soybean production and year-round spore production, whereas our winters help reduce spore buildups.”

Soybean rust needs the proper combination of temperature and moisture to survive and spread, Moore noted, with 68 to 77 degrees F. being optimum. Reproduction slows in either direction above or below that range and essentially stops at 95 degrees.

“The disease can only grow on living leaf tissue. Under optimum conditions, spores can penetrate leaves and infect them within six hours, but symptoms only become visible in the field seven to eight days later. The dilemma producers face is deciding if what they're seeing is rust or another problem.”

Soybean rust is hard to identify, Moore said. “The spores can't be seen unless you have at least a 35-power hand lens, so in most cases it's impossible to look at a field and say it has soybean rust. Samples have to be taken to the lab to be sure. Too many other diseases can cause symptoms that look like soybean rust.

“Producers should be constantly looking at their fields for something that looks different, beans that are defoliated, or other abnormal conditions. They should collect leaves and send them to the lab for analysis.”

Soybean sentinel plots have served a useful purpose in alerting southern U.S. growers to the presence and spread of the disease, Moore said.

“We started planting sentinel plots at the end of February and early March. Information from these plots and from scouting producer fields will be used to detect rust spores that may be blown in, and producers will be alerted.

“The best chances for overwintering in the U.S. are in warm coastal areas. For soybean rust to develop there must be present the fungus, wind movement to disperse it, and susceptible plants.”

It appears that moisture is a major factor in rust getting a foothold, he pointed out.

“In 2005, Mississippi was extremely hot and dry and there was little rust development. What can we expect in 2006? In February, there was a cold snap that dropped temperatures to 25 degrees on the Gulf Coast and chances are any spores were killed all the way down the state.”

Spores were found in kudzu patches in several locations in Florida in January, Moore noted, but mean air currents and weather conditions will be a major determinant in whether they are later spread across Georgia and Alabama into Mississippi fields.

Where producers had soybean rust last year, they obtained excellent control with fungicides, he said. “But they should pay attention to other problems, too. One producer was so concerned about a soybean rust problem that never showed up, that stink bugs took his crop.”

In 1970, an epidemic of southern corn blight resulted in a $1 billion loss to U.S. growers, he said. “It was a major disaster, but producers overcame the problem within one year, thanks to new varieties. Nobody can say if there will be a soybean rust epidemic in Mississippi, but we do know the disease can be managed effectively with timely fungicide applications.” These materials include:

Strobilurins, such as Headline and Quadris. “These are preventive materials and producers are likely to get enough yield increase from controlling other diseases to justify the cost of their use for soybean rust treatment.”

Triazoles, such as Tilt, Folicur, and Laredo, Bumper, Domark, and Propimax, which are penetrant/curatives and move within leaf tissue to kill the disease within the plant.

Mixes such as Quilt, Stratego, and Pristine.

Researchers have found 24 soybean breeding lines that look promising for some resistance, Moore said, but they are several years down the road. Presently, “100 percent of U.S. soybean varieties are susceptible. Soybean rust will be in the U.S. from now on and producers need to learn how to deal with it. Every crop has risk factors and we are trying to head this risk off as best we possibly can.”

The work done by Moore and other Mississippi Extension specialists and researchers has been “extremely valuable to producers,” says Mack Young, Extension director for Quitman County, Miss.

“A lot of producers were primed to go out and spray last year when they didn't need to. The timely information and advice provided throughout the season kept a lot of producers from spending money on treatments that weren't needed.”